Autism and the transsulfuration pathway


Dysregulation of the transsulfuration pathway has been implicated in autism with research showing homocysteine and and oxidized glutathione levels were significantly higher in children diagnosed with autism spectrum disorders while cysteine levels, total glutathione and glutathione were remarkably lower in childiren with autism spectrum disorder compared to control subjects. Homocysteine levels levels correlated significantly with increasing Childhood Autism Rating Scale scores.

Taurine is synthesized from l-cysteine. Taurine is involved in calcium homeostasis. Taurine levels in autistic children were lower than than in controls. There may be low taurine levels only in a subset of indivduals with autism. Not all studies show taurine levels are low in autism.

Research points to intracellular calcium homeostasis being dysregulated in autism. Genes for various sub-units of proteins that act as calcium channels are associated with autism. In autism dysregulation of the transsulfuration pathway could dysregulate taurine synthesis which could dysregulate calcium homeostasis.

Whatever the answer is increasing levels of L-cysteine through supplementing with L-cysteine containing amino acids is not the answer. L-cysteine containing amino acids can be very toxic.

CACNA1C (Cav1.2) and psychiatric disease

The calcium channel, voltage-dependent, L type, alpha 1C subunit is a protein that is encoded by the CACNA1C gene. Via calcium channels calcium influxes into cells. Mutations in CACNA1C are associated with bipolar disorder, depression, schizophrenia and autism. Gain of function mutations in CACNA1C are associated with disease, for example, autism.

Taurine regulates intracellular calcium levels by preventing influxes of calcium into cells but not effluxes of calcium out of cells. Via regulating influxes of calcium into cells taurine has a role in the treatment of psychiatric disorders that are in part due to gain of function mutations in CACNA1C.

Alzheimer’s disease and bone mineral density

Alzheimer’s disease patients are also at a higher risk for hip fractures than healthy controls. A meta-analysis indicated that the Odds Ratio for hip fractures in patients with Alzheimer’s disease is 1.80 compared to healthy controls. Low bone mineral density and increased loss rate of bone mineral density were associated with higher risk of Alzheimer’s disease.

There are a lot of illnesses where there are both high homocysteine levels and decreased bone mineral densities, for example, Alzheimer’s diseases. High homocysteine levels and decreased bone mineral densities in range of illnesses can be tied together by dysregulations of the transsulfuration pathway in such illnesses.

Bipolar disorder and bone mineral density

There are decreases in bone mineral density in drug naive individuals with bipolar disorder compared to age- and gender-matched healthy controls. Individuals with bipolar I disorder have have high homocysteine levels. High homocysteine levels in individuals with bipolar disorder point to the transsulfuration pathway being dysregulated. Via the transsulfuration pathway L-cysteine is synthesized from homocysteine. L-taurine is synthesized from L-cysteine.

Taurine is required for calcium homeostasis. Taurine, also, is conjugated to various bile acids. Bile acids are are required for absorption of fat-soluble vitamins. Vitamin D and vitamin K are fat-soluble vitamins. Individuals with bipolar disorder are 4.7 times more likely to be vitamin D deficient than individuals amongst the general population of the Netherlands, however, deficient levels of vitamin D are not specific to bipolar disorder but are also present in individuals with schizophrenia. The taurine transporter is present in osteoblasts. Osteoblasts synthesize bone.

With taurine metabolism dysregulated calcium homeostasis is dysregulated and absorption of vitamin D and vitamin K is decreased. Decreases in bone mineral density in bipolar disorder could be due to dysregulation of the transsulfuration pathway which dysregulates calcium homeostasis and vitamin D and vitamin K absorption resulting in low bone mineral density.